Investigations into the mechanisms of rock support provided by sprayed liners

Abstract:

An investigation into the mechanisms of rock support provided by sprayed
liners was carried out practically at three different mines, namely, South
Deep Mine (Gold Fields), Mponeng Mine (Anglo Gold Ashanti) and Impala
Platinum Mine (IMPLATS). The monitored sites included tunnels and
pillars supported by steel fibre reinforced shotcrete and plain shotcrete.
Underground monitoring provided information on the behaviour of
shotcrete over time as the pillars and tunnels responded to mining induced
stress changes. The exercise played a role in the identification of the
possible failure modes of shotcrete in-situ. Underground in-situ bond
strength tests were carried out to give an idea of the shotcrete-rock
interface bond strength. The monitoring methods included measurement
of strains and displacements of the tunnel walls and pillar walls with the
aid of Vibrating Wire Strain Gauges (VWSG), Multi-Point Borehole
Extensometers (MPBX), Single-Point Borehole Extensometers (SPBX)
and laser targets. Inspection boreholes were drilled, and monitored using
camera probes to observe the condition of the rock behind the shotcrete.
Also, photographs were taken to give an idea of the failure modes and
support mechanisms provided to the rock by shotcrete based on field
observations.
Fibre reinforced shotcrete laboratory tests were carried out according to
the EFNARC and ASTM standards for shotcrete panel and beam testing.
The laboratory tests helped in identifying the effects of fibre incorporation
into the shotcrete for the support of underground mining excavations.
The results obtained from the field monitoring exercise, field tests, and
laboratory tests were used to analyse and deduce the possible
mechanisms of rock support provided by sprayed liners in mining
excavations.